Hacker News Reader

Comment by qwertox | Hacker News Reader

I wonder if such strong IR light is capable of harming the eye, even if we're unable to see it.

High power LEDs in the visible spectrum are terribly bright, and when I accidentally get them shined into the eye, it really feels concerning if any harm has been done.

View on HN

Good question, this guy seems to have studied this question:

https://medium.com/@alex.kilpatrick/ir-illumination-and-eye-...

He concludes:

"If you buy the largest IR floodlight available on Amazon and you stare at it 200 mm (~7") from your face for more than 1000 seconds (~ 16 minutes) there is a possibility you might damage your cornea. So don’t do that. And I doubt anyone would do that because these things get pretty hot at that distance."

Near-IR aiming lasers (such as the AN/PEQ-2 and AN/PAQ-4) can indeed cause permanent damage, among USAF CATM armorers there was a rumor of at least one idiot burning his retina trying to "see" the beam directly.

We can stare at a burning campfire and barely get damaged. Long term exposure is another thing. The emitter power would have to be insanely high, or some kind of laser.

Yes, but a campfire emits a lot of visible light, so our eyes adjust accordingly. While we're not cats with their amazing pupil dilation, we have some too. If one wears an IR-shiny hood, they may be at higher risk in the low-light conditions, if their eyes adjust to the dark, brain not realizing they're flooded with IR.

Retinal damage is not the only kind of damage the eye can be subjected to. The cornea has no blood flow to cool itself and is fully exposed to incoming radiation.

A campfire has radiance limited by its temperature. It can put out a lot of power, but that power can't be focused to a high energy density at your retina. An LED can be nearly a point source, and can deposit a lot of power at a small spot, i.e., "almost a laser." Moreover, being invisible, an IR LED doesn't cause your pupil to close. And LEDs have gotten powerful enough to be dangerous. The regulations for optical radiation exposure now cover LEDs as well as lasers.

Aren't traditional (non-LED) lightbulbs that get hot much higher in the IR spectrum since they're dissipating most of their energy as heat?

Bright visible light causes the pupil to constrict and triggers an instinct to squint, blink, or look away. IR alone does not.

"Why do my eyes feel spicy?"

Reply on news.ycombinator.com